The present invention relates, in general, to semiconductor devices, and more particularly, to a novel method of forming an isolation area on a semiconductor device.
The semiconductor industry previously had utilized a thick field oxide in order to provide electrical isolation between the active areas of metal oxide semiconductor (MOS) transistors that existed on a semiconductor die. The thick field oxide increased the threshold voltage of any parasitic device which existed between the MOS transistors and prevented inadvertent electrical coupling between the transistors. As advances in semiconductor processing technology reduced both the width of the active area and the spacing between active areas to sub-micron dimensions, it became difficult to provide reliable isolation between the active areas. During the field oxide growth, portions of the active area became contaminated. Often, the field oxide encroached into the active area and prevented removal of the contamination. The contamination limited the transistor's gate oxide reliability, and also limited the gate oxide breakdown to an electric field strength of less than 8 Mv/cm.
Accordingly, it is desirable to have a method of forming a field oxide that provides a thick field oxide (greater than approximately 4000 angstroms), an active area that is substantially devoid of contamination resulting from the field oxide growth, a reliable gate oxide, and a high gate oxide breakdown (greater than approximately 8 Mv/cm).